If you do your online research and start to browse websites about making money with blogs, you're probably going to find a great deal of blogs full of ads telling you how their particular site makes money.
You'll roll your eyes, maybe read a line or two, and then see a cool, flashy ad that asks you to buy the Essential Blogging eBook that Explains It All for You.
You click on the ad and end up at another site, this time chock-full of huge banners telling you to buy similar products from the eBook advertised on the page.
Whether or not you've put dime one of your own money into buying the e-book, you've already helped two people make money from their blogs.
The two key factors to your monetary success in blogging for profit are traffic flow and revenue streams.
The more revenue streams you have directed at the site on which you put your blog-- from direct product endorsements someone paid you to put onto your blog, to an ad-sharing service like AdSense, to donation buttons placed on your blog-- the better the chance that you can leverage your blog for money to keep it-and yourself-going.
In order to build those streams of revenue, of course, you have to sign up for one of these ad-sharing services (Google's is free) and, more importantly, come up with something to write about that will interest people enough to both go to your site and to keep their friends coming in as well.
Of course, neither of those factors are very effective when your subject matter is general or dull.
In order to keep people reading your blog, clicking the ads on the blog, and coming back to your blog to do it again, you have to be writing about something that's entertaining to read.
So before you sign up for a Blogger or WordPress account and start dreaming about paying your mortgage with your witticisms, you need to figure out what sort of subject you want to write around that will keep you interested and in turn keep your potential readers interested, too.